An oxetane group-carrying methacrylate, 3-ethyl-3-(methacryloyloxy)methyloxetane (EMO), was polymerized via copper-mediated atom transfer radical polymerization (ATRP) initiated from the surface of monodisperse silica particles (SiPs). The polymerization proceeded in a living manner producing SiPs grafted with well-defined poly(EMO) (PEMO) of target molecular weight up to about 400K with a graft density as high as 0.36 chains/nm 2 . The surface-initiated ATRP of methyl methacrylate (MMA) with PEMO-grafted SiPs as macroinitiator afforded SiPs grafted with block copolymer of the type PEMO-b-PMMA ((PEMO-b-PMMA)-SiPs). The PEMO layer of (PEMO-b-PMMA)-SiPs, located between the PMMA shell and the SiP core, was cross-linked by cationic ring-opening reaction of the oxetane groups of the EMO moieties. The removal of the SiP core of the cross-linked (PEMO-b-PMMA)-SiPs by HF etching gave polymeric hollow spheres having size uniformity and good dispersibility in organic solvents.

A free radical initiation(R′OBR2) system is based on a combination of an alcohol (R′OH) initiator and a dialkylborane (HBR2) activator. Due to an empty p‐orbital in the B atom, the CO bond can be cleaved to form a reactive C• radical for initiating radical polymerization, while the stable •OBR2 radical remains inactive. Considering the large availability of various alcohol moieties, this asymmetric initiation chemistry can be applied to supermolecular structures and surface modifications.

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